Colistin resistance represents a mounting global health concern, particularly alarming in the face of multidrug-resistant (MDR) and extensively drug-resistant (XDR) bacterial infections. As a polymyxin-class antibiotic, colistin has long served as a critical last-line defence against severe Gram-negative infections caused by pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. However, its increasing and, at times, indiscriminate use has driven the emergence of resistant strains, thereby compromising its clinical utility.Mechanistically, colistin resistance arises from diverse genetic adaptations that alter the bacterial outer membrane, diminishing the drug's binding affinity. Prominent among these are modifications to lipopolysaccharides (LPS), including the incorporation of cationic groups that neutralise the membrane's negative charge, effectively impeding colistin interaction. In addition to chromosomal mutations, resistance is often mediated through horizontal gene transfer-most notably via mobile colistin resistance (mcr) genes-which facilitates rapid dissemination among bacterial populations.To counter this growing threat, innovative therapeutic strategies are urgently needed. These include the development of novel antibiotics with distinct mechanisms of action, synergistic combination regimens (e.g., colistin paired with potentiating agents), and the exploration of alternative modalities such as bacteriophage therapy. Gene-editing technologies like CRISPR-Cas9 also offer a promising frontier for targeting resistance determinants directly at the genetic level.Equally important are robust antimicrobial stewardship programmes and comprehensive surveillance systems to monitor resistance trends and guide rational antibiotic use. Ultimately, overcoming colistin resistance demands a multifaceted and integrative approach-one that merges scientific innovation with global public health initiatives.

• Keywords
• AMR, Colistin, Efflux pump, Mcr,
• Publication type
• Journal Article MeSH
• Review MeSH

BACKGROUND: Wastewaters are considered as important players in the spread of antimicrobial resistance, thus affecting the health of humans and animals. Here, we focused on wastewaters as a possible source of carbapenemase-producing Enterobacterales for the environment. METHODS: A total of 180 presumptive coliforms from hospital and municipal wastewaters, and a river in the Czech Republic were obtained by selective cultivation on meropenem-supplemented media and tested for presence of carbapenemase-encoding genes by PCR. Strains carrying genes of interest were characterized by testing antimicrobial susceptibility, carbapenemase production and combination of short- and long- read whole-genome sequencing. The phylogenetic tree including publicly available genomes of Enterobacter asburiae was conducted using Prokka, Roary and RAxML. RESULTS: Three VIM-producing Enterobacter asburiae isolates, members of the Enterobacter cloacae complex, were detected from hospital and municipal wastewaters, and the river. The blaVIM-1 gene was located within a class 1 integron that was carried by different F-type plasmids and one non-typeable plasmid. Furthermore, one of the isolates carried plasmid-borne colistin-resistance gene mcr-10, while in another isolate chromosomally located mcr-9 without colistin resistance phenotype was detected. In addition, the analysis of 685 publicly available E. asburiae genomes showed they frequently carry carbapenemase genes, highlighting the importance of this species in the emergence of resistance to last-line antibiotics. CONCLUSION: Our findings pointed out the important contribution of hospital and community wastewaters in transmission of multi-drug resistant pathogens.

• Keywords
• mcr, Antimicrobial resistance, Carbapenemase, Environment,
• MeSH
• Anti-Bacterial Agents pharmacology   MeSH
• Drug Resistance, Bacterial genetics   MeSH
• Bacterial Proteins genetics   MeSH
• beta-Lactamases * genetics   MeSH
• Enterobacter * genetics   drug effects   isolation & purification   MeSH
• Phylogeny MeSH
• Colistin * pharmacology   MeSH
• Humans MeSH
• Microbial Sensitivity Tests MeSH
• Wastewater * microbiology   MeSH
• Plasmids genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anti-Bacterial Agents MeSH
• Bacterial Proteins MeSH
• beta-Lactamases * MeSH
• carbapenemase MeSH Browser
• Colistin * MeSH
• Wastewater * MeSH
• VIM-1 metallo-beta-lactamase MeSH Browser

The aim of this study was to determine the occurrence of plasmid-mediated colistin resistance in domestic and imported meat and slaughter animals in the Czech Republic during 2020-2021 by using selective cultivation and direct PCR testing. A total of 111 colistin-resistant Escherichia coli isolates with mcr-1 gene were obtained from 65 (9.9%, n = 659) samples and subjected to whole-genome sequencing. Isolates with mcr were frequently found in fresh meat from domestic production (14.2%) as well as from import (28.8%). The mcr-1-positive E. coli isolates predominantly originated from meat samples (16.6%), mainly poultry (27.1%), and only minor part of the isolates came from the cecum (1.7%). In contrast to selective cultivation, 205 (31.1%) samples of whole-community DNA were positive for at least one mcr variant, and other genes besides mcr-1 were detected. Analysis of whole-genome data of sequenced E. coli isolates revealed diverse sequence types (STs) including pathogenic lineages and dominance of ST1011 (15.6%) and ST162 (12.8%). Most isolates showed multidrug-resistant profile, and 9% of isolates produced clinically important beta-lactamases. The mcr-1 gene was predominantly located on one of three conjugative plasmids of IncX4 (83.5%), IncI2 (7.3%), and IncHI2 (7.3%) groups. Seventy-two percent isolates of several STs carried ColV plasmids. The study revealed high prevalence of mcr genes in fresh meat of slaughter animals. Our results confirmed previous assumptions that the livestock, especially poultry production, is an important source of colistin-resistant E. coli with the potential of transfer to humans via the food chain. IMPORTANCE We present the first data on nation-wide surveillance of plasmid-mediated colistin resistance in the Czech Republic. High occurrence of plasmid-mediated colistin resistance was found in meat samples, especially in poultry from both domestic production and import, while the presence of mcr genes was lower in the gut of slaughter animals. In contrast to culture-based approach, testing of whole-community DNA showed higher prevalence of mcr and presence of various mcr variants. Our results support the importance of combining cultivation methods with direct culture-independent techniques and highlight the need for harmonized surveillance of plasmid-mediated colistin resistance. Our study confirmed the importance of livestock as a major reservoir of plasmid-mediated colistin resistance and pointed out the risks of poultry meat for the transmission of mcr genes toward humans. We identified several mcr-associated prevalent STs, especially ST1011, which should be monitored further as they represent zoonotic bacteria circulating between different environments.

• Keywords
• colistin, livestock, mcr, resistance, screening,
• Publication type
• Journal Article MeSH